I came across this monster for "only" € 9.500,00 (amazon.com sells it for $25,999.00)
Sigma 200-500mm F2.8 IF EX APO DG HSM Canon - Sigma 200-500mm F2.8 IF EX APO DG HSM Canon (http://www.fotokonijnenberg.nl/sigma-200-500mm-f2-8-if-ex-apo-dg-hsm-canon)
Including the 2.0x extender.